Source synchronous data transfer schemes have been used to increase data transfer rate as compared to common clocked data transfer schemes. While common clocked data transfer schemes use a common clock signal for devices on the sending and receiving ends of a data transfer, in source synchronous data transfer schemes, the sending device provides one or more strobe signals with the data being transferred. The receiving device uses the strobe signal to sample the incoming data.
In order to maximize data transfer, the sampling point as determined by the strobe signal should be in the center of the data time period. This provides a setup margin of one-half data period and a hold margin of one-half data period. The strobe signal can be centered by the sending device or by the receiving device. What is needed is method and apparatus to center strobe signals with respect to the data signals with which the strobe signals are transferred.